The new evidence includes eye witness testimony from defectors, video footage and Assad's private emails.

British television channel 4 on Monday was expected to air a story with fresh evidence that members of Syrian President Bashar Assad's family and inner circle are directly ordering the commission of crimes against humanity in Syria.

A Channel 4 investigation, "The Real Mr & Mrs Assad," reveals new evidence implicating top commanders, family members and henchmen of Assad. The new evidence both damages the regime by painting many of its top figures as war criminals, while also making future prosecution of Assad on charges of crimes against humanity a more realistic prospect, according to legal experts.

Defectors from Syrian intelligence and security agencies who previously were part of the regime's efforts to crush the 14-month-long revolt, told Channel 4 that the President's cousin issued "shoot-to-kill" orders against civilian protestors in Deraa in April last year. Snipers were reportedly given "Kill quotas," meaning they were expected to assassinate at least a minimum number of pro-democracy activists.

Notably, it is alleged that Assad's brother, Maher, a senior army commander, was part of a group of senior leaders at a secret command center in Deraa when the leadership ordered to crack down on a protest march by all means necessary. Over 100 civilians were killed. Maher is also accused of ordering indiscriminate collective-punishment of all of the men in the town of al-Moudamya, later in the same month.

The documentary further examines emails which indicate that the Assads knew the details of individuals being arrested for their political activities as part of the regime's crackdown. In at least two separate cases, the Assad's appear to have personally intervened to ensure that certain detainees were released.

Besides eye-witness testimony from various defectors, the documentary will screen footage of Assad and his wife, Asma, relaxing and joking together in 2009.

Importantly, the President says to Asma: "Every mistake [that] happens in this government, you are responsible, not somebody else. Not the minister. Not the Prime Minister. At the end you should be responsible." He was clearly referring to himself. This despite that in more recent months, Assad has repeatedly denied any role or advance knowledge of the killings.

"No one is authorized to give orders to the security forces except for him," says exiled former Syrian Vice-President Abdul Halim Khaddam, who fell out with Assad in 2005, having served under both him and his father. Khaddam added: "Will anyone believe that 300,000 soldiers can come out of their barracks to slaughter citizens due to an initiative by their officers? These orders are issued by the President of the state."

International law experts argue that it is "preposterous and completely implausible" to say that Assad did not have knowledge or was unaware that his security forces were perpetrating systematic and widespread killing and torture.

William Schabas, Professor of International Criminal Law at Middlesex University, said that even minus a "smoking gun" linking President Assad directly to the killings, he can be brought to trial and convicted based on the doctrine of Command Responsibility.

"There is very little evidence of Hitler ordering direct atrocities to be perpetrated. Does anyone have any doubt that Hitler wasn't in charge? I don't think so. And I think that this is a similar case, stated Schabas. "We can hold him responsible," Schabus says, "even if we can't prove that he actually ordered the crimes. Whether he is a micro-manager of atrocity, or whether he's a macro-manager, it doesn't actually make much difference."